Various types of printing machines use inking systems in which an ink supply roller is in contact with ink within an ink trough. Some ink supply rollers have a surface which is non-homogeneous, that is, non-uniform, for example formed with pores. One such machine--see U.S. Pat. No. 3,585,932--used an ink supply roller with a metallic surface which has open pores etched therein. The ink roller cooperates with a doctor blade made of plastic, which is shaped to a suitable profile at the side facing the ink supply roller. Etching the surface of the ink supply roller is expensive, and the doctor blade is subject to wear and can be readjusted to the edge shape only within narrow limits; thus, after the doctor blade itself is somewhat worn, it has to be exchanged and replaced.